{contact.display_name} token fails in Offline Event Registration mail (message Subject only)

We have edited our message templates to include the participant name in the subject (for many reasons, one of which is to prevent overlapping subject lines in our mailbox).

Unfortunately we are not able to use

of

in the subject of the Registration Confirmation and Receipt (off-line) message.

I have no clue why this template would be different in that respect but it seems desirable to be able to use the name token also in the offline registration mail. No clue on a solution yet.